With regard to an inverted pendulum-type traveling dolly and control method thereof, for example, there is known an art described in the Japanese Patent Laid Open Gazette 2004-295430.
In the Japanese Patent Laid Open Gazette 2004-295430, a traveling dolly is disclosed which has a wheel and a body supported by the wheel, a centroid of the body positioning above a rotation axis of the wheel. With regard to the traveling dolly, control at the dolly translation direction (the direction rectangular to the axis) including the inverted pendulum control and the position control and control at the dolly rotation direction (the turning direction of the axis) including only the position control are performed.
The traveling dolly has a control means calculating control command value to a drive means for the wheel (torque command value to a motor). The control means is so robust as to make the body stand invertedly stably against disturbance. Accordingly, even if the dolly located surface slopes or load is changed, the body can keep on standing stably.
With regard to the control at the dolly translation direction, wheel angle (rotation angle of the wheel relative to the body), wheel angular velocity which is a single derivative of the wheel angle, body tilt angle (tilt from the vertical direction) and body tilt angular velocity which is a single derivative of the body tilt angle are used as state quantities (observed quantities). Hereupon, the body tilt angle is instable so that the dolly cannot stand invertedly stably without feedback control. Accordingly, with regard to the control at the dolly translation direction, the control input is determined so as to make all the state quantities zero.
However, the control at the dolly translation direction disclosed in the Japanese Patent Laid Open Gazette 2004-295430 has one input (axle torque) and two outputs (wheel angle and body tilt angle) and uses the wheel angle and the body tilt angle so as to calculate the torque command value to the motor. Accordingly, trade-off (the relation that if one of conditions is satisfied, the other condition becomes dissatisfied) exists between the two outputs, and if the disturbance applied on the dolly is large, below problems may be caused.
Namely, since the control at the dolly translation direction has one input and two outputs as mentioned above, when the external force is applied on the body by the movement of the centroid caused by the change of position of an operator on the body, the fluctuation of centroid position caused by mounting a burden on the body, the operator riding on and off or the like, firstly, the axle torque is applied so as to make the body tilt angle fluctuated by the external force return to zero. The body tilt angle is stabilized accordingly and then the axle torque is applied so as to make the wheel angle zero, thereby returning the moved dolly to the initial position.
When the disturbance is small, the dolly slightly moves and stops at the initial position by the above-mentioned control. However, for example when the external force caused by the large disturbance which is stationary or changes transiently widely is applied on the body, the body tilt angle and the wheel angle cannot be made zero simultaneously, whereby the oscillation centering on the initial position (the position of the dolly before applying the disturbance thereon) is difficult to be converged. Accordingly, the position of the wheel is moved widely (the wheel angle is changed widely). Furthermore, according to the same reason, if an operator jumps on the traveling dolly or similar operation is performed on the dolly, the position of the wheel must be moved widely and an operator cannot get on and off easily.
Namely, in the dolly translation direction, if a heavy thing is mounted on a position difference from the centroid position of the body or an operator rides on the body and lifts a heavy thing by a suspension mechanism such as an arm provided on the upper portion of the dolly, the centroid position of the body is changed, whereby the dolly cannot stop at the initial position.
Considering such a traveling dolly as a mobile body on which an operator rides or which carries goods, the occurrence of large movement of the wheel position by the disturbance makes an operator difficult to get on and off and makes goods difficult to be taken on and off.
Accordingly, the purpose of the present invention is to provide control method of a traveling dolly and the traveling dolly which makes the movement of the dolly (a position of a wheel) minimum and enables stable position control in the case that large external force is applied on the dolly so that goods can be taken on and off easily and an operator can get on and off easily.